Certificate In iOS McSEssion

Question

In iOS MCSession, you can initialize the section using the following method initWithPeer:securityIdentity:encryptionPreference:

Most online tutorials the authors put nil for securityIdentity. However, I wonder whether any damage (hacked) if leaving nil for the real app. If so, how to generate a SecIdentityRef for this?

I found the following articles/discussions about Security in iOS, but still have trouble to connect SecIdentityRef with MCSession.

Thank you for precious time on my question, and any comment will be helpful.

1. Securing and Encrypting Data on iOS: http://code.tutsplus.com/tutorials/securing-and-encrypting-data-on-ios--mobile-21263

2. How to establish a SecIdentityRef in an iPhone keychain ? (Without a .p12): How to establish a SecIdentityRef in an iPhone keychain ? (Without a .p12)

3. Generate key pair on iphone and print to log as NSString: Generate key pair on iphone and print to log as NSString